It is well known to form components by casting methods using molten metals, and that the casting may deform as it cools due to shrinkage. In particular it may bend and/or twist as it cools. Where the casting is heat treated to remove inherent stresses built up in the casting as it was formed and cooled, the casting may further deform.
The dimensional accuracy of the component may be achieved by machining to the correct dimensions. However, because of the inherent strain in the component, this may result in further distortions as any weakened portions of the component yield to the inherent stresses. This makes machining difficult and increases cost and time and requires the part to have a greater level of restraint during machining.
Alternatively the component may be deformed by bending, pressing or other mechanical working method, literally forcing it to take up the desired shape. Mechanical working is very unsatisfactory as the mechanical strain introduced during manipulation is often found to relax over time. The consequence of this is that material of the component creeps during its operational life and hence the component may change shape and no longer conform to desired dimensions, despite it being dimensionally accurate upon completion of its manufacture. This results in operational non-conformance which is highly problematic for the functioning of mechanical hardware, especially those used for flight.
Mechanical working may introduce further residual strain in the component. For many applications the presence of high internal stress and strain will not be an issue.
However, for other applications it is, and may increase the chance of the component having a shortened operational life.
Typically this problem is resolved by either accepting the reduced life, or making the component from thicker material so that it can deal with higher loads (i.e., the operational load plus the residual stressed present in the component). However, increasing the material thickness may compound the problem.
Additionally, if the casting is large and rigid, the equipment required to mechanically work the component must be capable providing a great deal of force, and hence are highly specialist and expensive pieces of equipment (for example, large hydraulic presses.)
Hence a method and apparatus which enable the shaping or reshaping of cast components which do not increase the residual stress and/or strain in the component, and which does not require the use of expensive equipment is highly desirable.